[PATCH] nfs: prevent truncate on active swapfile

[PATCH] nfs: prevent truncate on active swapfile

[Omar Sandoval]

Most filesystems prevent truncation of an active swapfile by way of
inode_newsize_ok, called from inode_change_ok. NFS doesn't call either
from nfs_setattr, presumably because most of these checks are expected
to be done server-side. However, the IS_SWAPFILE check can only be done
client-side, and not doing so is dangerous.

Signed-off-by: Omar Sandoval <osandov-nWWhXC5lh1RBDgjK7y7TUQ@public.gmane.org>
---
 fs/nfs/inode.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index 4bffe63..9205513 100644
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -506,10 +506,15 @@ nfs_setattr(struct dentry *dentry, struct iattr *attr)
 		attr->ia_valid &= ~ATTR_MODE;
 
 	if (attr->ia_valid & ATTR_SIZE) {
+		loff_t i_size;
+
 		BUG_ON(!S_ISREG(inode->i_mode));
 
-		if (attr->ia_size == i_size_read(inode))
+		i_size = i_size_read(inode);
+		if (attr->ia_size == i_size)
 			attr->ia_valid &= ~ATTR_SIZE;
+		else if (attr->ia_size < i_size && IS_SWAPFILE(inode))
+			return -ETXTBSY;
 	}
 
 	/* Optimization: if the end result is no change, don't RPC */
-- 
2.2.0

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Re: [PATCH] nfs: prevent truncate on active swapfile

[Omar Sandoval]

On Thu, Dec 18, 2014 at 10:29:18PM -0800, Omar Sandoval wrote:
> Most filesystems prevent truncation of an active swapfile by way of
> inode_newsize_ok, called from inode_change_ok. NFS doesn't call either
> from nfs_setattr, presumably because most of these checks are expected
> to be done server-side. However, the IS_SWAPFILE check can only be done
> client-side, and not doing so is dangerous.
> 
> Signed-off-by: Omar Sandoval <osandov@osandov.com>
> ---
>  fs/nfs/inode.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
> index 4bffe63..9205513 100644
> --- a/fs/nfs/inode.c
> +++ b/fs/nfs/inode.c
> @@ -506,10 +506,15 @@ nfs_setattr(struct dentry *dentry, struct iattr *attr)
>  		attr->ia_valid &= ~ATTR_MODE;
>  
>  	if (attr->ia_valid & ATTR_SIZE) {
> +		loff_t i_size;
> +
>  		BUG_ON(!S_ISREG(inode->i_mode));
>  
> -		if (attr->ia_size == i_size_read(inode))
> +		i_size = i_size_read(inode);
> +		if (attr->ia_size == i_size)
>  			attr->ia_valid &= ~ATTR_SIZE;
> +		else if (attr->ia_size < i_size && IS_SWAPFILE(inode))
> +			return -ETXTBSY;
>  	}
>  
>  	/* Optimization: if the end result is no change, don't RPC */
> -- 
> 2.2.0
> 
Sorry, forgot to mention that this applies to Linus' tree as of today.

-- 
Omar